The present application claims priority to Japanese Patent Application No. 2002-10978 filed Jan. 21, 2002, the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a tandem scanning optical device, and more particularly, to a tandem-type scanning optical device that records an image on each of multiple photoreceptors based on exposure thereof via multiple deflected scanning laser beams in an image forming apparatus (such as a color laser printer or color digital copying machine), for example.
2. Description of the Related Art
Tandem scanning optical devices of the conventional art include a type of scanning optical device that records an image on each of multiple photoreceptors based on exposure thereof via scanning using laser beams deflected by the same surface of a deflector, such laser beams corresponding to multiple colors (such as the four colors of yellow (Y), magenta (M), cyan (C) and black (K), for example). A tandem scanning optical device of this type offers the advantages of faster scanning, a lower cost and a compact device size.
However, deflection of as well as scanning of photoreceptors by multiple laser beams using the same surface of a deflector without increasing the size of such deflector requires synthesis of the light paths of the laser beams before they strike the deflector and spatial separation of the light paths after the laser beams leave the deflector (the so-called synthesis/separation method). Therefore, a tandem scanning optical device is generally constructed such that the multiple laser beams strike the same surface of the deflector at different angles in the sub scanning direction (sub scanning direction). Because the incident angle and incident position are normally adjusted according to color, the problem arises that such a tandem scanning optical device has a high error sensitivity in connection with the scanning optical system (comprising elements such as fxcex8 lenses) disposed behind the deflector, and accordingly, complex and high-precision adjustment is necessary in order to obtain a prescribed level of performance.
A main object of the present invention is to provide a tandem scanning optical device that is capable of performing easily and with high precision adjustment of the incident angles and incident positions of the multiple beams that strike the same surface of the deflector.
In order to attain the above object, the tandem scanning optical device of the present invention is a tandem scanning optical device that deflects and causes multiple beams to scan in the main scanning direction and separates the light paths of such beams in the sub scanning direction by causing them to strike the same surface of a deflector at different angles in the sub scanning direction, such optical device including first adjustment mechanism that changes the angles of the multiple beams simultaneously in order to adjust the beam incident angles relative to the same surface of the deflector in the sub scanning direction and second adjustment mechanism that moves the multiple beams simultaneously in a parallel fashion in order to adjust the beam incident positions on the same surface of the deflector in the sub scanning direction.
The tandem scanning optical device may further include a light source unit that emits multiple beams and a reflective mirror that simultaneously reflects the multiple beams emitted from the light source. The first adjustment mechanism may comprise a mirror adjustment unit that adjustably changes the orientation of the reflective mirror, and the second adjustment mechanism may comprise a light source adjustment unit that adjustably moves the light source unit in a parallel fashion.
The mirror adjustment unit may have a construction in which the orientation of the reflective mirror is adjusted by tightening, using a movable screw, one end of the reflective mirror pressed by a plate spring.
The tandem scanning optical device may further include a light source unit that emits multiple beams and a housing in which the light source unit is fixed in place, such light source unit having multiple legs the lengths of which can be changed in order to position the light source unit relative to the housing, wherein the legs serve as the first adjustment mechanism when the lengths of some of the legs are changed by a different amount from the remaining other legs, and as the second adjustment mechanism when the lengths of all of the legs are changed by the same amount.
The invention itself, together with further objects and attendant advantages, will best be understood by reference to the following detailed description taken in conjunction with the accompanying drawings.